A number of saturated fluorocarbon compounds and azeotropes are commonly used as refrigerants in refrigeration systems. The various refrigerants have different physical constants, such as boiling points and vapor pressures, which dictate their suitability for a particular use. Refrigerant systems are generally classified as either high pressure or low pressure depending upon the contained pressure. In many refrigeration systems a small amount of oil is circulated with the refrigerant and its presence is considered in the designing of the systems. Also, refrigerants and oil absorb moisture to a degree so that some water is usually present. The refrigerant goes between the liquid and vapor states in the refrigeration cycle. Contaminants in the refrigerants may also be considered as liquid or vapor in that their dew points are relatively close to those of the refrigerants and can possibly condense and vaporize in the cycle. To treat a contamination problem, it is first necessary to identify the contaminant(s) present. In testing refrigerants in a closed system, it can thus be generally assumed that the refrigerant, at ambient temperature, can be at a pressure ranging from about 20 psig to over 200 psig, depending upon the refrigerant, and that some oil and water will be present. In addition, contaminants such as the reaction products of the chemical reactions between the refrigerant, lubricant, moisture, residual solvents, solder, flux, electrical insulation materials, etc. may be present and the contaminants and refrigerant may be in the liquid or vapor state. If a closed refrigeration system is to be tested to determine the presence of contaminants, the normal procedure is to remove the refrigerant from the system and test it for water. The lubricant from the compressor is tested for acids, etc. in a separate test.
The presence of excess moisture in the system can be due to faulty drying of equipment at the factory and in service operations, leaks in the system, oxidation of hydrocarbons, wet oil and/or refrigerant and decomposition of cellulose insulation in hermetically sealed units. The presence of excess moisture can cause ice formation in the expansion valves and capillary tubes, corrosion of metals, copper plating and chemical damage to insulation in hermetic compressors. Acid can be present due to motor burnouts which cause overheating of the refrigerant. Such burnouts can be temporary or localized in nature as in the case of a friction producing chip which causes a local hot spot which overheats the refrigerant. The main acid of concern is HCl but other acids and contaminants can be produced as the decomposition products of oil, insulation, varnish, gaskets and adhesives.